class Solution {
public:
    char findTheDifference(string s, string t) {
        int buffer[26]={0};
        for(int i=0;i<s.length();i++){
            buffer[s[i]-'a']--;
            buffer[t[i]-'a']++;
        }
        buffer[t[t.length()-1]-'a']++;
        int idx;
        for(int i=0;i<26;i++){
            if(buffer[i]>0){idx=i;break;}
        }
        return idx+'a';
    }
};